Breast biopsy under conscious sedation
The following case will emphasize conscious sedation and its potential complications.
· general pre-operative evaluation
· sedative agents
· respiratory depression: detection, management
· mask ventilation
· laryngeal mask airway
· reversal of sedation.
The patient, a 40-year-old and otherwise healthy woman, comes for breast biopsy.
This procedure is usually performed in two stages: first a radiologist places a nee-dle percutaneously into the lump. Next, the patient reports to the operating room for removal of the lump, pathologic confirmation of the margins, and perhaps a larger procedure depending on the circumstances.
History: She has no chronic medical problems but recently detected a lump in her right breast. Needle localization was performed in radiology this morning and she now presents to the operating suite for lumpectomy.
This healthy patient requires very little additional anesthetic work-up. We ask about the following:
(i) a brief review of systems, including gastro-esophageal reflux disease (negative)
(ii) past surgical procedures (none)
(iii) family history of anesthetic problems (none)
(iv) current medications, including over-the-counter herbal remedies (none)
(v) allergies, including latex (none)
(vi) habits including smoking, alcohol and drugs (none)
(vii) physical examination, including airway:
Nervous white woman in no acute distress; weight 60 kg; height 5 4 (165 cm) BP120/80 mmHg; HR 80 beats/min; respiratory rate 12 breaths/min
Airway: Mallampati I, 4 fingerbreadth(fb) mouth opening, 4 fb thyromental distance,
full neck extension
CV: S1, S2 no murmur
Respiratory: Lungs clear to auscultation
Dressing with needle in right breast.
pre-operative laboratories and studies (none are indicated) This healthy patient would be classified as ASA 1.
Anesthetic preparation: We discuss the risks/benefits of the various anesthetic options. She selects i.v. sedation and we administer an anxiolytic (midazolam (Versed®) 2 mg i.v.).
The surgeon will inject a local anesthetic, blunting the majority of the pain from the procedure, while the anesthesiologist is present to observe and reassure the patient, administer additional anxiolytics or opioids, and treat any hemodynamic instability. Most patients prefer not to be awake and aware during such a pro-cedure. Anesthetic options include (i) conscious sedation, in which the patient remains arousable and in control of her own airway, but free from anxiety and generally unaware of the procedure, and (ii) general anesthesia in which the air-way must be managed by mask, laryngeal mask airway or endotracheal tube. After we explain the risks to the patient, she selects i.v. sedation.
Establishment of sedation: Once in the operating room, we apply standard monitors (non-invasive blood pressure, ECG, pulse oximetry), taking care to avoid the right arm for blood pressure cuff application in case axillary node dissection becomes necessary. Following a 50 mg bolus of propofol, we start an infusion at 50–80 mcg/kg/min. The patient’s saturation declines to 95% so oxygen via nasal cannula is applied at 4L/min and the saturation rapidly returns to 100%.
In order to obtain a therapeutic blood level rapidly, we give an initial bolus of propofol and follow it with a continuous infusion to maintain the level of seda-tion. When the patient is sufficiently drowsy, positioning, prepping and draping can commence. While it should not be necessary, everyone in the room must be reminded the patient is “awake.” This includes a sign on the door for those entering later. Unfortunately, the decorum of the OR is not routinely suitable for the awake patient. As in any workplace, discussions may depart from the task at hand, causing concern for a patient who is aware, and might recall irrelevant or objectionable talk.
Maintenance of anesthesia: We titrate the propofol infusion to the desired effect with a goal of arousability with slurred speech, but respiratory and hemodynamic stability.
During injection of local anesthetic into the breast, she complains of pain. We administer fentanyl 50 mcg, and increase the propofol infusion rate. One minute later the patient moans and we respond with another 50 mcg fentanyl. Fifteen minutes later the SpO2 is falling rapidly. On examination we discover she is apneic. We start ventilation by mask, but encounter difficulty maintaining an open upper airway. When things do not get much better after placing an oral airway, we insert a laryngeal mask airway (LMA) and achieve good air movement. Her saturation rebounds rapidly.
Less than 2 mcg/kg fentanyl should not cause apnea. Alone, that is usually true, however opioids combined with sedatives act synergistically to depress ventila-tion. Had we been monitoring respiratory pattern/rate we would have noticed that her breathing became dangerously slow a couple of minutes after we had given fentanyl. Our detection method (pulse oximetry here) failed us because we gave so much supplemental oxygen that her PaO2 was probably close to 200 mmHg as long as she was breathing, if slowly. Thus she had to be almost apneic for her PaO2 to fall below 80 mmHg, where a drop in the SpO2 would be expected.
In this case a smaller dose of fentanyl might have been more appropriate, or perhaps the use of a shorter acting opioid such as remifentanil. More importantly, we should monitor respiratory rate, either via a precordial stethoscope (imprac-tical for this particular surgical procedure) or by a capnograph attached through the nasal cannula. At the first sign of oversedation, we could have breathed for her and administered a reversal agent (naloxone). However the side effects of reversal must also be considered, particularly in the middle of an operation.
In managing the apnea, several issues need be recognized. If the problem is central, e.g., oversedation impairing respiratory drive, the patient’s lungs will have to be manually ventilated. If soft tissue obstruction of the upper airway is to blame, we need to establish an open airway with the help of an oral airway or LMA. In this difficult phase of being neither awake nor completely anesthetized, manipulation of the upper airway can lead to laryngospasm, coughing, vomiting, and significant movement (usually much to the dismay of the surgeon). In our case the problem was central depression and the patient tolerated the LMA. At this point we usually add nitrous oxide and increase the propofol infusion rate so she will continue to tolerate the device. This increased sedation is limited by the need to have her resume spontaneous ventilation.
Emergence from anesthesia: During closure of the incision, we titrate down the propofol and eventually discontinue the nitrous oxide. When the bandage has been applied, and the patient is awake and breathing with a good respiratory pattern, we suction the posterior pharynx and remove the LMA.
Post-anesthesia care. There should be little pain from this procedure. We turn the care of the patient over to the postanesthesia care unit (PACU) nurses with standing orders of morphine for pain, and an anti-emetic, as needed.
One advantage of the LMA is that, if the patient is breathing spontaneously but not fully awake, she can be transported to the PACU with the LMA in place, where the nurse removes it at the appropriate time.
Discharge: When the patient is fully awake and tolerating oral intake, she can be dis-charged home with a caregiver, prescription for an analgesic and instructions not to drive for 24 hours.
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